1. Field of the Invention
The present invention relates to a polypropylene resin composition and an injection-molded article thereof. More specifically, it relates to a polypropylene resin composition exhibiting a superior pigment dispersibility and an injection-molded article thereof.
2. Description of Related Arts
Polypropylene resins are widely used as materials requiring rigidity, impact strength and the like. In recent years, molded articles molded from a composition comprising a polypropylene resin by injection molding or the like, have begun to be used particularly as materials for automobiles. Such molded articles are required to have mechanical properties, such as rigidity and impact strength, as well as good appearance such as to provide an integral appearance unified with an automobile body, an upgraded image, and high design properties or the like. As such a composition, there is known a composition composed of an ethylene-propylene block copolymer, a rubber such as an ethylene-xcex1-olefin copolymer rubber or an aromatic vinyl-containing rubber, used to improve the impact resistance, talc used to improve the rigidity, and a pigment master batch used for coloring.
For instance, JP08-134278A discloses a compound for molding composed of a propylene-xcex1-olefin block copolymer resin, a modified polyolefin, a pigment, a pigment dispersant, a silane coupling agent, a rubber component, and an inorganic filler; and a compound for molding composed of a propylene-xcex1-olefin block copolymer resin, a pigment, a pigment dispersant containing amodifiedwax, a silane coupling agent, a rubber component, and an inorganic filler. Specifically, there are disclosed a compound in which a maleic anhydride graft polypropylene is used as the modified polyolefin, and a compound in which a maleic acid-modified polyethylene wax is used as the modified wax contained in the pigment dispersant.
JP10-60182A discloses a composition composed of a polyolefin, a filler, a pigment, and an olefin-based polymer wax. Specifically, there is discloses a composition containing a polyethylene wax or a polypropylene wax as the olefin-based polymer wax.
Molded article molded from these polypropylene resin compositions by injection molding, however, sometimes have a portion that appears to be different in color from the rest at a molded article surface formed just at the back of the gate or at a molded article surface on an extension of the gate in a part in which the wall thickness changes and, therefore, the appearance thereof is often damaged. This is considered to be caused by insufficient dispersion of the pigment resulting from differences in pigment concentration and talc concentration at a part of the surface portion of the molded article which occur due to separation or agglomeration of the ingredients of the composition during the injection molding.
In view of the foregoing circumstances, the inventors of the present invention have made intensive study and, as a result, found that the foregoing problems can be solved by a specific polypropylene resin composition containing a specific polypropylene composition and a pigment master batch having a specified hydrogen ion concentration and a specified viscosity xcex7pig(poise).
An object of the present invention is to provide a polypropylene resin composition excellent in pigment dispersibility.
Another object of the invention is to provide an injection molded article of said composition, suitable for automobile exterior and interior parts.
Other objects and advantages of the present invention will be apparent from the following description.
That is, the present invention relates to a polypropylene resin composition comprising:
100 parts by weight of a polypropylene-based composition (D) comprising 50% to 95% by weight of a polypropylene resin (A), 0% to 25% by weight of an ethylene-xcex1-olefin copolymer rubber and/or aromatic vinyl compound-containing rubber (B), and 5% to 25% by weight of talc (C) having an average particle diameter of not more than 3 xcexcm; and
0.5 to 8.0 parts by weight of a pigment master batch (E) having a hydrogen ion concentration of 5 to 7 and satisfying the expression: 0.35xe2x89xa6xcex7pig/xcex7compxe2x89xa61.20, wherein the xcex7pig represents a viscosity (poise) of the pigment master batch, and the xcex7comp represents a viscosity (poise) of the polypropylene-based composition (D), and to an injection-molded product thereof.
The present invention will be described in detail below.